CBSE Class 10 Science 2022 · Paper 31/4/3 · Question 14

(a) A galvanometer is an instrument that detects the presence of a current in a circuit; its pointer stays at zero (the centre of the scale) when no current flows and deflects to the left or right of zero depending on the direction of the current. As the magnet moves towards the coil, the magnetic field through the coil changes; this changing field induces a potential difference across the coil, which sets up an induced current through the galvanometer, so its needle deflects, only while the magnet is moving. (b) No deflection is observed: the needle stays at zero. The coil and the magnet move together, so there is no relative motion between them; the magnetic field through the coil does not change, so no current is induced. (c)(i) Conclusion: a changing magnetic field, produced here by moving the magnet relative to the coil, induces a current in the coil (electromagnetic induction), and the current lasts only while the field keeps changing. Yes, the momentary deflection increases: with more turns and a stronger magnet moved in the same way, a larger current is induced, so the needle deflects further. OR (c)(ii) Electromagnetic induction is the process by which a changing magnetic field induces a current in a conductor. With a strong bar magnet held stationary near one end of the coil, the galvanometer shows no deflection, because the magnetic field through the coil, though present, is not changing, so no current is induced.